Piezoelectric ink droplet ejecting device

Abstract

A piezoelectric ink droplet ejecting device drivable with a low voltage, simple in structure, less costly to manufacture and capable of producing printed data with high resolution. A piezoelectric ink droplet ejecting device has a plurality of ink ejectors each composed of a piezoelectric transducer for varying the volume of an ink passage to eject ink out of the ink passage. A single piezoelectric ceramic panel which is polarized in a thickness direction has a plurality of through holes parallel to the polarized direction. The through holes serve as ink passages. When a driving electric field is applied in a direction perpendicular to the polarized direction, the piezoelectric ceramic panel is elastically deformed under thickness shear effect, thus varying the volume of the ink passages to eject ink droplets therefrom.

What is claimed is: 
     
       1. A piezoelectric ink droplet ejecting device having a plurality of ink ejectors each composed of a piezoelectric transducer for varying a volume of an ink passage to eject ink out of the ink passage, the device comprising: the piezoelectric transducer made of a piezoelectric material and polarized in a longitudinal direction, the piezoelectric transducer being formed with a plurality of the ink passages extending longitudinally therethrough in a direction parallel to the polarized direction, the piezoelectric transducer being elastically deformable to vary the volume of the ink passages to eject ink stored therein in response to a drive electric field applied perpendicularly to the polarized direction in each of the ink passages.   
     
     
       2. The piezoelectric ink droplet ejecting device as claimed in claim 1, wherein the piezoelectric transducer comprises a pair of upper and lower piezoelectric ceramic panels bonded together, the upper piezoelectric ceramic panel being polarized in a first direction along the polarizing direction and being formed with through holes for serving as the ink passages, and the lower piezoelectric ceramic panel being polarized in a second direction opposite the first direction along the polarizing direction and being formed with through holes contiguous with the through holes of the first panel for serving as the ink passages. 
     
     
       3. The piezoelectric ink droplet ejecting device as claimed in claim 1, wherein the piezoelectric transducer has side walls defined between the ink passages adjacent with each other, each of the side walls being dimensioned to satisfy the relationships H≧L and L/W≧3 where W is the width of the side wall in a direction of the drive electric field, L the length of the side wall, and H the depth of the side wall in the polarized direction. 
     
     
       4. The piezoelectric ink droplet ejecting device as claimed in claim 1, wherein the piezoelectric transducer has side walls defined between the ink passages adjacent to each other, the side walls being inclined to an array direction such that those side walls which confront each other in the array direction intersect with each other. 
     
     
       5. The piezoelectric ink droplet ejecting device as claimed in claim 1, wherein the plurality of ink passages are formed in a two-dimensional array in the piezoelectric transducer. 
     
     
       6. The piezoelectric ink droplet ejecting device as claimed in claim 2, wherein the ejector further comprises: an orifice plate joined to an upper surface of the upper piezoelectric ceramic panel, the orifice plate being formed with a plurality of ink orifices in communication with the through holes; and   a bottom plate joined to a lower surface of the lower piezoelectric ceramic panel, the bottom plate being formed with a plurality of ink supply passages in communication with the through holes.   
     
     
       7. The piezoelectric ink droplet ejecting device as claimed in claim 2, wherein the through holes have circular cross-section, and are arranged in a geometrical pattern having symmetric hexad axes. 
     
     
       8. The piezoelectric ink droplet ejecting device as claimed in claim 2, wherein the through holes have hexagonal cross-section, and are arranged in a geometrical pattern having symmetric hexad axes. 
     
     
       9. The piezoelectric ink droplet ejecting device as claimed in claim 2, wherein the through holes have circular cross-section, and are arranged in a geometrical pattern having symmetric tetrad axes. 
     
     
       10. The piezoelectric ink droplet ejecting device as claimed in claim 3, wherein the piezoelectric transducer comprises a pair of upper and lower piezoelectric ceramic panels bonded together, the upper piezoelectric ceramic panel being polarized in a first direction along the polarizing direction and being formed with through holes for serving as the ink passages, and the lower piezoelectric ceramic panel being polarized in a second direction opposite the first direction along the poralizing direction and being formed with through holes contiguous with the through holes of the first panel for serving as the ink passages. 
     
     
       11. The piezoelectric ink droplet ejecting device as claimed in claim 3, wherein the ejector further comprises: an orifice plate joined to an upper surface of the upper piezoelectric ceramic panel, the orifice plate being formed with a plurality of ink orifices in communication with the through holes; and   a bottom plate joined to a lower surface of the lower piezoelectric ceramic panel, the bottom plate being formed with a plurality of ink supply passages in communication with the through holes.   
     
     
       12. The piezoelectric ink droplet ejecting device as claimed in claim 3, wherein the through holes have rectangular cross-section, and are arranged in two horizontal rows and four vertical columns for providing eight ejectors. 
     
     
       13. The piezoelectric ink droplet ejecting device as claimed in claim 3, wherein the side walls are inclined to an array direction such that those side walls which confront each other in the array direction intersect with each other. 
     
     
       14. The piezoelectric ink droplet ejecting device as claimed in claim 4, wherein the through holes has isosceles triangle cross-section for providing the side walls intersecting with each other, and for providing other side walls extending in the array direction. 
     
     
       15. The piezoelectric ink droplet ejecting device as claimed in claim 14, wherein neighboring isosceles triangular through holes are oriented reversely by 180 degrees. 
     
     
       16. The piezoelectric ink droplet ejecting device as claimed in claim 15, wherein the through holes are arranged in a matrix of two horizontal rows and eleven vertical columns for providing twenty-two ink passages. 
     
     
       17. The piezoelectric ink droplet ejecting device as claimed in claim 16, wherein each corner of the isosceles triangular through hole is rounded in shape.